A variety of optical communications modules are used in optical networks for transmitting and receiving optical data signals over the networks. An optical communications module may be an optical receiver module that has optical receiving capability, but not optical transmitting capability. Alternatively, an optical communications module may be an optical transmitter module that has optical transmitting capability, but not optical receiving capability. Alternatively, an optical communications module may be an optical transceiver module that has both optical transmitting and optical receiving capability.
A typical optical transmitter or transceiver module has a transmitter optical subassembly (TOSA) that includes a laser driver circuit, at least one laser diode and various other electrical components. The laser driver circuit outputs an electrical drive signal to each respective laser diode to cause the respective laser diode to be modulated. When the laser diode is modulated, it outputs optical signals that have power levels corresponding to logic 1s and logic 0s. An optics system of the module focuses the optical signals produced by each respective laser diode into the end of a respective transmit optical fiber held within an optical connector module that connects to the optical transmitter or transceiver module.
A typical optical receiver or transceiver module has a receiver optical subassembly (ROSA) that includes at least one receive photodiode and various other electrical components. An optics system of the ROSA focuses an optical data signal that is output from the end of an optical fiber onto a photodiode of the ROSA. The photodiode converts the incoming optical data signal into an electrical analog signal. An electrical detection circuit, such as a transimpedance amplifier (TIA), receives the electrical signal produced by the photodiode and outputs a corresponding amplified electrical signal, which is processed by other circuitry of the ROSA to recover the data.
One well known type of optical communications module is a TO-can assembly. FIG. 1 illustrates a perspective view of one known TO-can assembly 2 having a typical TO-can assembly configuration. The TO-can assembly 2 includes a header 3, a ring 4, a cap 5, a collar 6, and a receptacle 7. The header 3, the ring 4, the cap 5, the collar 6, and the receptacle 7 are typically made of a metal material, such as stainless steel, for example, to allow them to be welded together. The TO-can assembly 2 is generally cylindrical in shape. The header 3 has an upper mounting surface 3a on which a TOSA and/or a ROSA and other electric components are mounted. These components are internal to the ring 4 and therefore are not visible in FIG. 1. Electrical leads (not shown) or electrical contacts (not shown) are disposed on a lower surface 3b of the header 3 for electrically interconnecting the TOSA or ROSA of the assembly 2 to external electrical circuitry, such as electrical circuitry of a printed circuit board (PCB) (not shown). A portion of a flexible (flex) circuit is sometimes mounted on the header 3, in which case the electrical and optoelectronic components of the TO-can assembly are mounted on the flex circuit and electrically connected thereto.
The ring 4 has a first end 4a and a second end 4b. The second end 4b of the ring 4 is fixedly secured to the upper surface 3a of the header 3. The cap 5 has a first end 5a and a second end 5b. The second end 5b of the cap 5 is fixedly secured to the first end 4a of the ring 4. The collar 6 has a first end 6a and a second end 6b. The second end 6b of the collar 6 is fixedly secured to the first end 5a of the cap 5. The receptacle 7 has a first end 7a and a second end 7b. The second end 7b of the receptacle 7 is seated within and fixedly secured to the first end 6a of the collar 6. The receptacle 7 is a tube-like structure that receives a portion of an optical fiber (not shown) that is passed through the first end 7a of the receptacle 7 and secured therein. The optoelectronic component (not shown) mounted on the upper surface 3a of the header 3 may be either an optoelectronic light source, such as a laser, or an optoelectronic light sensor, such as a photodiode, depending on whether the TO-can assembly 2 contains a TOSA or a ROSA, respectively.
The optical axis of the TO-can assembly 2 is represented by dashed line 8. If the TO-can assembly 2 contains a TOSA, light emitted by the laser diode (not shown) of the TOSA propagates along the optical axis 8 into the end of the optical fiber (not shown). If the TO-can assembly 2 contains a ROSA, light passing out of the end of the optical fiber propagates along the optical axis 8 and is received by the photodiode of the ROSA.
Prior to fixedly securing the collar 6 to the cap 5 and securing the receptacle 7 to the collar 6, the position of the collar 6 in an X-Y plane of an X, Y, Z Cartesian Coordinate system is adjusted to optically align the end of the optical fiber secured within the receptacle 7 with the laser diode or photodiode of the TOSA or ROSA, respectively. Once optical alignment in the X-Y plane has been achieved, the position of the receptacle 7 along the Z-axis, which corresponds to the optical axis 8, is adjusted to achieve the desired focus. For example, in the case of a TOSA, the position of the receptacle 7 along the Z-axis is adjusted until the optical beam emitted by the laser diode is brought to a focal point on the end of the optical fiber. In the case of a ROSA, the position of the receptacle 7 along the Z-axis is adjusted until the optical beam passing out of the end of the optical fiber is brought to a focal point on the light-receiving portion of the photodiode. Once the proper Z-axis alignment has been achieved, the second end 7b of the receptacle 7 is fixedly secured to the first end 6a of the collar 6.
A laser welding process is typically used to fixedly secure the receptacle 7 to the collar 6 and to fixedly secure the collar 6 to the cap 5. A projection welding process is typically used to fixedly secure the cap 5 to the ring 4. Projection welding typically forms a hermetic seal, whereas laser welding typically does not form a hermetical seal. Because a hermetical seal is needed between the cap 5 and the ring 4, projection welding is typically used for this purpose.
It can be seen in FIG. 1, that the receptacle 7 of the TO-can assembly 2 has a relatively long length, L, in the Z-dimension. The length, L, is about 0.75 inches. Because of the relatively long length, L, of the receptacle 7, the TO-can assembly 2 is not suitable for use in many modules due to spatial constraints. Consequently, TO-can assemblies of the type shown in FIG. 1 are limited to use in modules that are capable of accommodating the long lengths of their receptacles. It would be desirable to provide a TO-can assembly that has greater versatility with respect to spatial constraints so that it may be used in a wider range of applications and environments.